Front outputs are no task at all. Acquire the seal (OEM would be my preference and get a stake nut too). Remove the front driveshaft at the t-case (4 bolts), slide it out of the way. Un-stake the stake nut (chisel or sharp punch), remove stake nut, slide off flange (be prepared for flud to come out, its a good time for a fluid R&R). Remove seal (seal puller works best), carefully install new seal, install flange (cleanup splines and put a bit of silicone on them). Install nut, torque to spec (FSM's are online otherwise I can look it up out of the book for you). Re-stake nut, reinstall driveline and fill with fluid.
Keeping the flange from free-spinning while removing and torquing the nut can be a feat. Either make a tool that will bolt to a couple of the driveline bolt holes on the flange or its also possible to put the vehicle in 4WD and have someone stand on the brakes with the vehicle in gear while you spin it off.